1. Field of the Invention
This invention relates to a plasma generating apparatus and a plasma generating method. More particularly, the present invention relates to a plasma generating apparatus which can generate a stable and uniform glow discharge even in the air under the atmospheric pressure and also to a plasma generating method using such an apparatus.
2. Related Background Art
Various techniques have been developed to generate electric discharges under the atmospheric pressure. Such techniques are generally categorized as the silent discharge, the creeping discharge, the pulse corona discharge and so on. (The silent discharge is known as an ozone generator.) The creeping discharge is a technique in which electrodes are formed respectively on the surface and in the inside of an inorganic substance typically made of a ceramic material and then an electric discharge is generated on the surface of the ceramic material by applying an AC electric field between the electrodes. The pulse corona discharge is a technique of generating a corona discharge in an inter-electrode space by applying an ultra-short pulse high voltage with a half width of 50 to 500 nsec, which has a quick plasma rising time of 10 to 50 nsec at the electrodes.
However, the above listed known discharge apparatus and discharge methods can be accompanied by the following problems.
The silent discharge requires the use of a large number of reactors in order to establish a stable electric discharge in volumes of gas because the gap separating the electrodes of the discharge apparatus is as small as several millimeters.
The creeping discharge takes place only within a highly limited area.
The pulse corona discharge requires the use of a discharge apparatus whose power source and electrodes are costly.
There has also been proposed a technique of stably generating a glow discharge under the atmospheric pressure by means of specifically designed electrodes for the discharge apparatus. However, the proposed technique requires the use of helium or argon gas that is costly and can generate a stable glow discharge only in a limited area under the atmospheric pressure.
In view of the above problems of the known discharge techniques, it is therefore an object of the present invention to provide an apparatus and a method that can stably generate a plasma discharge at low cost and also a gas processing method using a plasma reaction. Another object of the present invention is to provide an apparatus and a method that can stably generate a plasma discharge under atmospheric pressure without using costly helium or argon gas as well as a low cost gas processing method using a plasma reaction for decomposing organic compounds or the like that are ordinarily hardly decomposed.
According to the present invention, the above objects are achieved by providing a plasma generating apparatus comprising a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, in which an inorganic dielectric substance containing barium titanate as a principal component is filled between the electrodes.
According to the present invention, there is also provided a plasma generating apparatus comprising a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, in which an inorganic dielectric substance with a dielectric constant between 1,000 and 10,000 is filled between the electrodes.
In another aspect of the present invention, there is provided a plasma generating method comprising steps of filling an inorganic dielectric substance containing barium titanate as a principal component between a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, introducing a gas between the electrodes and applying an AC electric field between the electrodes by means of the AC power source to generate a glow discharge under the atmospheric pressure.
According to the invention there is also provided a plasma generating method comprising steps of filling an inorganic dielectric substance with a dielectric constant from 1,000 to 10,000 between a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, introducing a gas between the electrodes and applying an AC electric field between the electrodes by means of the AC power source to generate a glow discharge under the atmospheric pressure. For the purpose of the invention, the gas contains air as a principal ingredient and may contain an organic compound or a chlorine-containing organic compound.
In still another aspect of the present invention, there is provided a gas processing method comprising the steps of filling an inorganic dielectric substance containing barium titanate as a principal component between a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, introducing a gas containing an organic compound between the electrodes and applying an AC electric field between the electrodes by means of the AC power source to generate a glow discharge under the atmospheric pressure, thereby decomposing the organic compound.
According to the invention, there is also provided a gas processing method comprising the steps of filling an inorganic dielectric substance with a dielectric constant from 1,000 to 10,000 between a pair of electrodes of an electrode connected to an AC power source and a grounded electrode, introducing a gas containing an organic compound between the pair of electrodes and applying an AC electric field between the electrodes by means of the AC power source to generate a glow discharge under the atmospheric pressure, thereby decomposing the organic compound.
Thus, a plasma generating apparatus, a plasma generating method and a gas processing method utilizing a plasma reaction of the present invention can generate a glow discharge under the atmospheric pressure by filling the inorganic dielectric substance between a pair of electrodes.
Additionally, when a granular inorganic dielectric substance is used, gaps are produced among the granules of the inorganic dielectric substance, which makes it possible to stably generate a uniform glow discharge with a low power consumption rate even if the gas is oxygen or nitrogen that requires a high firing voltage because the gaps are considerably small. Thus, it is no longer necessary to use costly gas such as helium or argon.
Still additionally, according to the invention, an electric discharge occurs in every gaps among the granules of the inorganic dielectric substance. Then, it is no longer necessary to use a large number of reactors. Furthermore, a plasma generating apparatus according to the invention can be manufactured at low cost because it can generate an electric discharge by means of an AC power source with a commercial frequency of 50 Hz.
Furthermore, according to the invention, a gas containing an organic compound that can be hardly decomposed by any known ordinary gas processing method can easily be decomposed into substances that are safe and can be treated with ease, by using the plasma reaction.